1. Field of the Invention
This invention relates to a control system for electrical apparatus and, in particular, to a system which can be manually programmed with relative ease.
2. Prior Art
Formerly, there were available several types of "controllers" useful in controlling the various components of an industrial electrical system. Earlier forms included a number of hard-wired panels arranged in a rack or the like, whose functioning could be changed, but only by relatively laborious, expensive and time-consuming changes in the interconnecting or addressing cables. Moreover, these control systems were relatively large and employed electromechanical components such as relays which use a relatively large amount of power and are subject to well-known problems of mechanical and electrical malfunction.
A later type of controller for this purpose involves a main controller having a number of electromechanical or electrical circuits to whose input the input devices such as push-buttons, limit switches, etc. are coupled and to whose output devices such as the solenoids and motor starters of the field apparatus are coupled. These systems also employ a programming terminal, usually with a display device, which permits the operator so instanteously modify the interconnections on the main controller in accordance with a desired ladder diagram, for example. The ladder diagram is instantaneously shown on the display. While these later systems represent a considerable improvement over the earlier, hard-wired systems, insofar as flexibility and ease of reprogramming are concerned they are quite expensive and beyond the budget of smaller industrial plants.
It is therefore among the objects of the present invention to provide a manually-programmable controller for industrial and other similar applications which is relatively inexpensive, simple to use, yet allows a great diversity of ladder-diagram-equivalent circuits to be changed or programmed with little difficulty. Those changes are immediately symbolized and displayed understandably on the apparatus itself.
Another of the objects of the invention is to provide a low voltage, low power system for programming a controller manually by using modules which are easily plugged into the system for producing a circuit operation therein which corresponds to the symbol on the module, all of the symbols together constituting a conventional ladder diagram of the equivalent operations.